Acoustic processing method and means



1966 J. v. BOUYOUCOS 3,233,872

ACOUSTIC PROCESSING METHOD AND MEANS Driginal Filed Sept. 20, 1962 75 J (T i 77 IN VENTORV JOHN M. BOUYOUCOS F1 A N BY 2 ATTORNEY United States Patent Ofiice 3,233,872 Patented Feb. 8, 1956 3,233,872 ACOUSTIC PROCESSING METHOD AND MEANS John V. Bouyoucos, 1t) Blossom Circle E,

Rochester, NX. Continuation of application Ser. No. 225,162, Sept. 20, 1962. This application Jan. 15, 1965, Ser. No. 427,211 Claims. (Cl. 259-4) This application is a continuation of copending application Serial No. 225,162, filed by applicant on September 20, 1962, now abandoned.

This invention relates to a method and means for acoustically processing fluids by employing the phenomenon of cavitation.

-It has been found that fluids, or mixtures of solids and fluids, may be emulsified, homogenized, dispersed or otherwise processed by making use of cavitation, which is a phenomenon wherein cavities filled with vapor and gas are formed in a fluid under the influence of a negative pressure or tensile stress and then collapse, often With violent effects, as the pressure is caused to become positive. Cavitation events are frequently accompanied by temperatures in the gas phase suflicient to produce lumi nescence and shock waves emanating from the collapse point throughout the surrounding liquid. The high local temperatures and shock pressures can produce both chemical and physical effects.

Unfortunately, the high energy associated wtih cavitation events can also produce an erosive action on the surfaces in contact with or surrounding the fluid; in a relatively short period of time, the walls of the fluid container may become pitted until, finally, total destruction of the container may result.

In order to maintain the cavitation process away from the Walls of the container, various proposals have been adopted, such as the use of focused acoustic energy,-and resort to standing wave phenomena to position the region of maximum tension away from solid interfaces. Such techniques usually require high frequencies in order to keep the chamber dimensions within reason. In liquid processing it is often desirable to take advantage of the greater cavitation energies associated with low frequencies, and still keep the eroding'action away from the walls of a fluid container of moderate size.

In accordance with the invention, acoustic energy from an acoustic vibration generator is superimposed upon a hydrostatic pressure field which, by virtue of the configuration of the fluid container and the steady motion of the fluid, has a region of minimum hydrostatic pressure distant from the container walls. The processing chamber configuration can be in the form of a ventu'ri through which the fluid to be processed can flow and wherein the region of minimum cross-section (throat) is a region of minimum axial pressure. The hydrostatic pressure may be reduced further in the central region of this throat by causing the fiuid to rotate and undergo a centrifugal-like flow. The combination of the axial and centrifugal flows thus produces a region of minimum hydrostatic pressure in the fluid along the axis of the throat region. If, now, in the absence of acoustic excitation, the minimum hydrostatic pressure along the axis of the throat region is just above the threshold of cavitation, then upon superimposing an acoustic pressure field throughout the container, cavitation may be generated and localized in the central region of the throat, or in the region of maximum tension, and may be maintained away from the container walls. Furthermore, the number of cavitation events produced during the traversal of the fluid through the throat of the acoustic processing chamber will depend upon the frequency of the acoustic energy supplied and velocity of flow through the throat. By proper selection of the fiow velocity and acoustic frequency, a sufiicient number of cavitation events may be caused to occur in the throat region to effect uniform processing of the through flow.

While it is true that for sufiiciently high flow velocities cavitation may be made to occur in the region of minimum pressure of the venturi section in the absence of acoustic excitation, the cavitation 50 produced is not readily and precisely controllable. Furthermore, the number of cavitation events occurring Within a fluid element passing through the throat in the absence of an acoustic field within the fluid is usually not sufiicient to effect uinform processing.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the drawing wherein:

The figure illustrated is a central cross-section view of an embodiment of the invention illustrating an acoustic vibration generator. coupled to an acoustic processing chamber through which a fluid is circulated under pressure.

A typical acoustic generator for supplying acoustic energy to a fluid processing chamber 50 is indicated in the drawing by the reference numeral 10. The acoustic generator It may be, for example, an acoustic vibration generator such as illustrated and described in detail in an application for US. Letters Patent, Serial No. 88,164 of John V. Bouyoucos, filed February 9, 1961, entitled Acoustic Vibration Generator and Coupler. Such generators convert hydraulic flow energy into acoustic energy when a fluid medium flowing under pressure in a closed path is modulated repetitively by a valve. The valve, which reciprocat'es within a cooperating stationary port structure, causes modulation of the flow through orifices formed between opposite ends of the valve and juxtaposed portions of the port structure. The fluid passing into and from oscillator chambers disposed in the fluid path is alternately accelerated and decelerated, causing pressure variations within these chambers. By appropriate design, these pressure variations may be made to react upon the valve in such phase relative to the motion of the valve as to sustain the valving action. These pressure variations, in addition, give rise to acoustic energy which can be extracted from either one or both of the oscillator chambers and transferred by way of coupling means, such as a radiating element to an external load. a

As indicated in the drawing, a fluid medium is introduced under pressure into oscillator chambers 15 and 16 by way of inlet line 17 connected to the high pressure side of a fluid pump 30 and thence through branch lines 18 and '19 communicating with respective oscillator chambers 15 and 16. The fluid then exits through annular orifices formed between opposite ends of valve 20 and adjacent portions of port structure 22 The fluid is returned to the low pressure side of pump 30 by way of discharge cavity 23 and outlet line 24. The oscillatory movement of the piston 25 and the attached radiating element 27, as driven by acoustic pressures developed within chambers 15 and 16. delivers acoustic energy to the fluid to be processed which is directed by means of one or more pumps 40A, 40B, etc., through the acoustic processing chamber 50. The amplitude of the acoustic energy supplied to the fluid within the acoustic processing chamber 50 may be varied, for example, by altering the supply pressure of the fluid pump 30.

The acoustic processingchamber 50 may be coupled acoustically to the generator 10 in the following manner. The housing 28 of the acoustic generator 10 and the wall 52 of the acoustic processing chamber 50 may be provided with respective flanges 29 and 53 which are attached to one another by appropriate fastening means 55. O-ring 32 is provided for preventing fluid flow from the processing chamber 59 past the radiating element 27 of the acoustic generator 1%. The processing chamber 50 is provided with a fluid inlet 57 and a fluid outlet 58, both of which are connected by appropriate hydraulic circuitry to one or more fluid pumps 40A, 4013, etc. As shown in the drawing, more than one body of fluid may be processed simply by. connecting a like number of pumps to the corresponding fluid body. For example, the fluid in receptacle 61 may be pumped by means of pump 40A into processing chamber 50 when valve 71 is open, while fluid in receptacle 62 may be pumped by means of pump 40B into the chamber 5% when valve 72 is open. Obviously, any number of bodies of fluid may be mixed in chamber 50. The direction of fluid flow is indicated by the arrows. The processed fluid is discharged into a container 66.

The wall 52 of the acoustic processing chamber 50 is tapered internally so as to form a venturi-like section 75 having a throat 77. The inlet 57 is mounted to the chamber 50 so that the fluid is introduced into the chamber tangentially to the walls thereof. A rotation coaxial to the longitudinal axis of the chamber 50 is thereby imparted to the fluid and the centrifugal forces thereby exerted on the fluid produce a pressure gradient trans verse to the longitudinal axis of the chamber which changes from a maximum near the wall of the chamber to a minimum at or near the center of the chamber. Rotation of the fluid can be achieved also by means of an impeller 8t) positioned within the chamber 50 and driven by a motor '(not shown) located externally of chamber 50 and connected to the impeller by a shaft 82 passing through a hydraulic seal 83 at the inlet end of the chamber. Both methods of imparting rotation to the fluid may be used alternatively or in conjunction. The inlet end of the chamber 50 is provided witha suitable acoustic termination which may .be in the form of an acoustic short circuit or reflector 78.

The result of the veturi section 75 being placed in the path of the fluid flow in chamber 50 is that the hydrostatic pressure at the throat77 is the lowest at any point in the system. The velocity of flow through the throat of the venturi may be so chosen that the hydrostatic pressure in the throat is just above the threshold at which cavitation will occur. If an acoustic signal from the acoustic generator 1t? is then superimposed upon the fluid within chamber 5i), cavitation can be madeto occur in the throat portion, since the net pressure will be least at this point due to the superimposition of the negative acoustic signal upon the already reduced hydrostatic pressure. To insure maximum pressure reduction at the throat, the system dimensions should be chosen with respect to the driving frequency so that the distance from the throat 77 to the end boundaries 27 and 78 of the processing chamber 50' in conjunction with the terminal impedance provides maximum pressurevariation at the throat.

In addition, by having the fluid cyclone rapidly, as by injecting it tangentially to the chamber wall, or by means of spinning vanes of an impeller, centrifugal forces will create a further pressure reduction transverse to the axis of the chamber. As a result, the vweakest region in the -fluidthe pointof lowest pressure in .the systemwi1l occur Within a cigar-shaped region along the axis of the venturi and away from the wall. This region of minimum pressure, indicated approximately by the reference numeral 90, away from the wall, is achieved by means of the three dimensional geometry of the steady flow which creates a hydrostatic pressure minimum for the acoustic field to act upon in order to cavitate the fluid.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art.

What is claimed is:

1. An acoustic processing system comprising an acoustic processing chamber having a longitudinal axis, means for passing fluid to be processed through said chamber along said longitudinal axis thereof, said chamber having an axial configuration of boundaries which provide an intermediate region for relatively high axial fluid velocity and consequent relatively reduced hydrostatic pressure in said intermediate region, means for imparting rotation to said fluid about said longitudinal axis to obtain further'reduction of hydrostatic pressure within a portion of said fluid when contained within said intermediate region but isolated from the boundaries of said chamber, the hydrostatic pressure of said portion of said fluid when within said intermediate region being slightly above the threshold of cavitation in the absence of acoustic energy in said chamber, and means connected to said acoustic chamber for controllably supplying acoustic energy to said fluid to cavitate said portion of said fluid when in said intermediate region of said chamher.

2. An acoustic processing system as set forth in claim 1 wherein said means for controllably supplying said acoustic energy includes a movable radiating element partially bounding said chamber and spacedfrom said intermediate region.

'3. An acoustic processing system for processing a plu rality of distinct bodies of fluids, said system comprising an acoustic processing chamber having a longitudinal axis, a plurality of distinct sources of fluids to be processed, means for selectively and controllably injecting fluid from said sources of fluids to be processed through said chamber along the longitudinal axis thereof to form a fluid mixture, said chamber having an axial configuration of boundaries which provide an intermediate region for relatively high axial fluid velocity and consequent relatively reduced hydrostatic pressure insaid intermediate region, means for imparting rotation to said fluid mixture about said longitudinal axis to obtain a further reduction of hydrostatic pressure within a portion of said fluid mixture when contained within said intermediate region but isolated from the boundaries of said chamber, the hydrostatic pressure of said portion of said fluid mixture when Within said intermediate region being slightly above the threshold of cavitation in the absence of acoustic energy in said chamber, and means coupled to said acoustic processing chamber for controllably supplying acoustic energy to said fluid mixture to cavitate said fluid mixture when in said intermediate region of said chamber.

4. An acoustic processing system for processing a fluid, said system comprising, an acoustic processing chamber having a longitudinal axis, said chamber. also having a venturi-like region dividing said chamber into first and second sections along said longitudinal axis, fluid supply means connected to one of said first and second sections of said acoustic processing chamber for passing said fluid underpressure through said acoustic processing chamber, means. for imparting rotation to saidfluid when in said acoustic chamber about the longitudinal. axis thereof, whereby said fluid has an axial and centrifugal flow when flowing through said venturi-like section of said chamber, and means connected tothe other one of saidfirst and second sections for controllably supplying acoustic energy to said fluid when in said processing chamber to cause said fluid to cavitate in said venturi-like region of said acoustic processing chamber.

-5. An acoustic processing system for processing a fluid, said system comprising, an acoustic processing chamber having a longitudinal axis, said chamber also having a venturi-like region dividing said chamber into first and second sections along said longitudinal axis, fluid supply means connected to one of said first and second sections of said acoustic processing chamber for passing said fluid under pressure through said acoustic processing chamber, means for imparting rotation to said fluid when in said acoustic chamber about the longitudinal axis thereof, whereby said fluid has an axial and centrifugal flow when flowing through said venturi region so that said fluid in said venturi region is under greater tension in said region than elsewhere in said chamber, and means connected to the other one of said first and second sections for controllably supplying acoustic energy to said fluid in said processing chamber to cause said fluid to cavitate when in said venturi region of said acoustic processing chamber.

6. An acoustic processing system comprising:

(a) an acoustic processing chamber having a longitudinal axis,

(b) first means for passing fluid to be processed through said chamber along said longitudinal axis thereof,

(c) said chamber having an axial configuration of boundaries which provide an intermediate region for relatively high axial fluid velocity and consequent relatively reduced hydrostatic pressure in said intermediate region,

(d) second means for imparting rotation to said fluid about said longitudinal axis to obtain further reduction of hydrostatic pressure within a portion of said fluid when contained within said intermediate region but isolated from the boundaries of said chamber, the hydrostatic pressure of said portion of said fluid when contained within said intermediate region being slightly above the threshold of cavitation in the absence of acoustic energy in said chamber,

(e) third means connected to said acoustic processing chamber for controllably supplying acoustic energy to said fluid to cavitate said portion of said fluid when in said intermediate region of said chamber, and

(f) said third means including a radiating element disposed along said longitudinal axis and spaced a given distance from said intermediate region and con stituting another boundary for said chamber.

7. An acoustic processing system as set forth in claim 6 wherein said third means includes an acoustic vibration generator coupled to said radiating element.

' 8. An acoustic processing system for processing a plurality of distinct bodies of fluids, said system comprisingt (a) an acoustic processing chamber having a longitu dinal axis,

(b) a plurality of distinct sources of fluids to be processed,

(c) first means for selectively and controllably inject ing fluid from said sources of fluids to be processed through said chamber along the longitudinal axis thereof to form a fluid mixture,

(d) said chamber having an axial configuration of boundaries which provide an intermediate region for relatively high axial fluid velocity and consequent relatively reduced hydrostatic pressure in said intermediate region,

(e) second means including an impeller for imparting rotation to said fluid mixture about said longitudinal axis to obtain a further reduction of hydrostatic pressure within a portion of said fluid mixture when contained within said intermediate region but isolated from said boundaries of said chamber, the hydrostatic pressure of said portion of said fluid mixture when contained within said intermediate region being slightly above the threshold of cavitation in the absence of acoustic energy in said chamber, and

(f) third means coupled to said acoustic processing chamber for controllably supplying acoustic energy to said fluid mixture when in said intermediate region of said chamber,

(g) said third means including a radiating element disposed along said longitudinal axis and spaced from said intermediate region and constituting another boundary for said chamber.

9. An acoustic processing system for processing a fluid,

said system comprising:

(a) an acoustic processing chamber having a longitudinal axis,

(b) said chamber also having a venturi-like region dividing said chamber into first and second sections along said longitudinal axis,

(0) fluid supply means connected to one of said first and second sections of said acoustic processing chamber for passing said fluid under pressure through said acoustic processing chamber,

(d) rotation means for imparting rotation to said fluid when in said acoustic chamber about the longitudinal axis thereof, whereby said fluid has an axial and centrifugal flow when flowing through said venturi like section of said chamber, and

(e) acoustic vibration means including a radiating element connected to the other one of said first and second sections for controllably supplying acoustic energy to said fluid when in said processing chamber to cause said fluid to cavitate in said venturi-like region of said acoustic processing chamber,

(f) said radiating element substantially constituting one end of said chamber.

10. An acoustic processing system as set forth in claim 9 wherein said rotation means is a rotary impeller disposed along said axis.

11. In the method of cavitating a fluid with the aid of a venturi, the steps comprising:

- (a) rotationally flowing said fluid through said venturi to derive a centrifugal-like flow, and

(b) applying acoustic energy to said fluid.

12. A method of cavitating a fluid with the aid of a 'venturi, the steps comprising:

(a) pumping said fluid continuously through said venturi, (b) rotating said fluid continuously in said venturi in a direction normal to the flow of said fluid through said venturi, (c) applying acoustic energy to said fluid in said venturi. 13. A method of treating a fluid in a housing including a chamber having a venturi region which defines a longitudinal axis, the steps comprising:

'(a) flowing a stream of said fluid through said chamber and through said venturi thereof, (b) rotating said stream of said fluid about said axis, (c) applying acoustic energy to said stream of said fluid within said venturi region to cavitate said fluid. "14. A method of treating a fluid in an acoustic processing chamber having a venturi-like region disposed along a longitudinal axis thereof to define a path for said fluid, the steps comprising:

(a) flowing said fluid under pressure through said path, -(b) imparting rotation to said fluid in said chamber about said axis to induce axial and centrifugal flow of said fluid along said path, and (c) supplying acoustic energy to said fluid along said path. 15. A method of treating a fluid in an acoustic processing chamber having an axial configuration of boundaries which provides an intermediate region for relatively high axial fluid velocity and consequent relatively reduced hy- 7 8 drostatic pressure in said intermediate region, the steps (c) applying'acou'stic energy to said flow of said fluid comprising: to cavitate said portion of said fluid. (a) passing said fluid continuously through said chameber to derive an axial flow of said fluid through said References Cited y file Examiner chamber having said reduced hydrostatic pressure 5 UNITED STATES PATENTS at said intermediate reg-ion, v n (in) rotating said axial flow of said fluid about its own n axis to induce a combined axial and centrifugal-like 2632634 3/1953 7 Williams 259 1 flow of said fluid to further reduce said hydrostatic pressure in a portion of said-fluid within said inter- 10 WALTER A. SCHEEL, Primary Examiner. rnedla'te region, and 

12. A METHOD OF CAVITATING A FLUID WITH THE AID OF A VENTURI, THE STEPS COMPRISING: (A) A PUMPING SAID FLUID CONTINUOUSLY THROUGH SAID VENTURI, (B) ROTATING SAID FLUID CONTINUOUSLY IN SAID VENTURI IN A DIRECTION NORMAL TO THE FLOW OF SAID FLUID THROUGH SAID VENTURI, (C) APPLYING ACOUSTIC ENERGY TO SAID FLUID IN SAID VENTURI. 